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Heat Waves

2022 DEC 1

Preliminary   > Disaster Management   >   Disasters   >   Disaster risk reduction

Why in news?

  • As per recent World Bank report, from 2030 onwards, more than 160 to 200 million people could be exposed to a lethal heat wave in India every year, and around 34 million Indians will face job losses due to heat stress-related productivity decline.

About Heat Waves:

  • Qualitatively, heat wave is a condition of air temperature which becomes fatal to human body when exposed.
  • Quantitatively, it is defined based on the temperature thresholds over a region in terms of actual temperature or its departure from normal.

What is criterion for declaring heat wave?

  • Heat wave is considered if maximum temperature of a station reaches at least 40 0C or more for Plains and at least 300 C or more for Hilly regions.
    • a) Based on Departure from Normal
      • Heat Wave: Departure from normal is 4.5 0 C to 6.4 0 C
      • Severe Heat Wave: Departure from normal is >6.4 0 C
    • (b) Based on Actual Maximum Temperature
      • Heat Wave: When actual maximum temperature ≥ 45 0 C
      • Severe Heat Wave: When actual maximum temperature ≥47 0 C
  • If above criteria met at least in 2 stations in a Meteorological sub-division for at least two consecutive days and it declared on the second day.

What is a criterion for describing Heat Wave for coastal stations?

  • When maximum temperature departure is 4.5 0 C or more from normal, Heat Wave may be described provided actual maximum temperature is 37 0 C or more.

What is the period of heat wave over India?

  • It is occurring mainly during March to June and in some rare cases even in July.
  • The peak month of the heat wave over India is May.

Areas prone:

  • Heat wave generally occurs over plains of northwest India, Central, East & north Peninsular India
  • As per the IMD, the most heatwave prone states are Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Odisha, Madhya Pradesh, Rajasthan, Gujarat, Vidarbha, and parts of Karnataka, Andhra Pradesh, Telangana, and occasionally over Tamil Nadu and Kerala.


Which of the statements given above is/are correct regarding Heat Waves?

1. The heat wave is considered when the maximum temperature of a station reaches at least 30°C for Plains

2. The peak month of the heat wave over India is May

Select the correct answer using the code given below:

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2